Since the 19th century, advanced machines have been developed and marked as human civilization. Invention of power machines such as heat engines was the beginning of modern machine manufacturing and the great industrial revolution was arisen. Building a more complex machine at the micron or even nanometer level is the ultimate goal of the ascendant nano-science. The realization of this goal may trigger a new round of industrial revolution, which will bring profound and huge impact to human society. Nanomotor is a power-assisting machine in nanometer scale. It is a pioneer of nano-machinery, and its importance can be regarded as the position of steam engine in the industrial revolution. Whitesides et al. discovered the first synthetic catalytic motor, it was able to convert chemical energy into its own kinetic energy.
However, artificial nanomotors are still in infancy stage, compared to the diversity of macroscopic motors that are almost ingrained in all aspects of technology. How to build more complex nanomotors to complete more complex work is still a challenge for researchers. In recent years, the application of automatic micro motors in the field of biomedicine has made great progress, converting energy into mechanical motion to promote its directional motion, which gives hope for the development of micro robots and nano robots. In this regard, people have worked on the manufacture of nanomotors, allowing motors to be propelled through different mechanisms, such as self-electrophoresis, diffusion electrophoresis, bubble propulsion, and external stimuli (such as light, ultrasonic electromagnetic fields, and local electric fields). This has led to the emergence of various nanomotors, such as nanowires, rods, spherical Janus micro motors, and tubular microjets, which have been used to detect ions, bio-imaging, manipulate drug delivery and cell separation, and intracellular advancement. In addition to biomedicine, nanomotors have some unexpected applications and technologies. Recently, nanomotors have also been used to move in contaminant solutions and perform required sensing and cleaning activities in environmental field.
On the other hand, photocatalytic technology is a new technology using sunlight and discovered in the 1970s, which excites transfer of electrons and holes in the catalyst under light, thereby having a strong oxidative ability to degrade organics. At present, photocatalyst have been applied in various fields such as environmental purification, self-cleaning, medical treatment, and antibacterial.
Since the photocatalyst must reach nanometer level to effectively express the photocatalytic performance, the photocatalyst is required to a nanometer size. This leads to problems as following:
(1) When the photocatalyst is irradiated under light, a plurality of electron-hole pairs are generated inside and on the surface of the photocatalyst. Due to the extremely short time, majority of the plurality of electron-hole pairs are combined and quench before diffusing to the surface. This leads to low catalytic efficiency of the photocatalyst in actual applicant.
(2) Since the photocatalyst in nanometer scale are easy to agglomerate, the surface area of the photocatalyst is reduced, which is not good for separation of electron and hole, resulting in catalytic activity greatly reduced and low photocatalytic efficiency.
(3) The photocatalyst can be used with a limited carrier. When it is supported on an inorganic carrier, the effective catalytic area is a plane and small, therefore the catalytic efficiency is low. When it is supported on an organic carrier, the photocatalyst is likely to cause photo-corrosion to the organic carrier, and the photocatalyst would loss, resulting in waste and a secondary pollution.
(4) Due to nanometer scale of the photocatalyst, the photocatalyst is difficult to be recycled and reused after catalytic reaction, which is likely to cause secondary pollution.